Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In mathematics, the eccentricity, denoted e or varepsilon, is a parameter associated with every conic section. It can be thought of as a measure of how much the conic section deviates from being circular. For every conic section, there exists a fixed point F, a fixed line L and a non-negative number e such that the conic section consists of all points whose distance to F equals e times their distance to L. F is called the focus of the conic section, L its directrix and e its eccentricity.